For seventy years, epidural procedures, first by single injection, then with needles and catheters, have been used to block labor pain. By placing an anesthetic solution not in the fluid-filled spinal canal, but in the epidural space outside it, sufficient localization can be achieved, when helped by characteristics of the anesthetic and features of the anatomy, to block spinal nerve trunks carrying pain from involved structures to the spinal cord without interfering with nerve functions which should remain intact to mediate labor or other processes. While epidural anesthesia is the commonest method of controlling childbirth today in most developed countries, it can disappoint the patient and physician alike by being variable in its effectiveness from one patient to another, or by interrupting to a degree the important labor functions: (1) increasing the need for cesarean section or instrumental delivery with vacuum extractor or forceps,--with their potential of increasing morbidity, or (2) creating an additional risk when depression of labor mechanisms are superimposed on a medical or obstetric difficulty accompanying, or arising in, labor.